Rahil,
As you probably know the ISEB Diploma in Business Analysis is part of BCS and consists of 4 certificates and 1 oral exam.
The 4 certificates are:
1. Requirements Engineering
2. Business Analysis essentials
3. Organisational Context
4. Modeling Business Processes (this is one of a small set of certificates you can chose for the fourth certificate but seems the most relevant).
These exams have to be taken with an exam provider as ISEB themselves no longer offer public exams. The exam providers are usually training organisations and while some may offer the facility for you to just take the exam a word of warning: the exams are all structured as scenarios and half a dozen or so questions designed to get you to DO business analysis on the scenario. As the training companies have written these exam papers and marking schemes (which have to be sanctioned by ISEB) they are inevitably using the terminology and style of the training organisation who wrote it. The upshot is that unless you approach BA in the same way that the training orgainisation that wrote the exam teaches it, you may struggle.
I can send you a couple of ISEB style questions (made up and not sanctioned by ISEB) and will happily mark it and explain to you the rationale for the marking (I have written and marked ISEB exam papers). Alternatively there are practice papers on the BCS website which have the marking schemes with them.
You will need to know formal concepts of, defintions for and how to apply techniques to model and elicit Objectives, Requirements (General, Business, Functional, Non-Functional, Technical, Detailed), process models, data models, business activity models, stragetic and organisational analysis, and a whole load of technical terms and concepts such as knowledge types, project approaches, the SDLC and BAs contribution to it and so on. There are books I can suggest on some of this if you want and BCS will suggest them as well.
The oral exam must be taken with ISEB themselves and is a 45-ish minute discussion on a project you did Business Analysis on to demonstrate your in depth application of the tools and techniques.
Hope some of the above helps.
I would be keen to know WHY you want to take the exams and your expactations for the benefits of having the Diploma...
Guy